The corrosiveness of a material treated with a fire retardant composition is a problem that has long needed a solution. This problem is of prime importance to the construction industry, which uses steel fasteners with fire retarded wood. Hence, by production of a fire retarded wood with low corrosion, the integrity of a structure made using this wood will not be undermined by corrosion failure of the steel fasteners.
Aqueous solutions of phosphate salts containing a corrosion inhibitor are known. These corrosion-inhibited solutions are illustrated by U.S. Pat. No. 3,223,649 to Langguth and U.S. Pat. No. 3,257,316 to Langguth et al.
Prior art fire retardant compositions containing water soluble sources of P.sub.2 O.sub.5 and NH.sub.3 are exemplified by U.S. Pat. No. 3,245,904 to Young and U.S. Pat. No. 4,038,451 to Brown et al. Young describes non-corrosive and corrosive solutions of his compositions, and Brown et al state that the compositions thereof tend to be less hygroscopic than prior art compounds and are less corrosive in metal containers.
Fire retardant compositions that additionally contain a water soluble source of B.sub.2 O.sub.3 are illustrated by U.S. Pat. No. 1,030,909 to Mesturino, U.S. Pat. No. 1,382,618 to Blenio, U.S. Pat. No. 1,793,357 to Brown, U.S. Pat. No. 2,386,471 to Jones et al, U.S. Pat. No. 2,526,083 to Nielsen, U.S. Pat. No. 2,538,199 to Jefferson et al, U.S. Pat. No. 2,901,427 to Steppe and U.S. Pat. No. 2,935,471 to Aarons et al. Blenio describes a composition that typically contains sulfuric acid, but may in one embodiment contain phosphoric acid, boracic acid and a neutralizing amount of ammonia. Jones et al state that the formulation thereof should be non-hygroscopic and should not cause excessive rusting or corrosion of nails or other metal parts. Nielsen states that treated vegetable products obtained by use of his composition exhibit practically no corrosive effects to ferrous metals placed in contact with the treated materials. The Jefferson et al patent is directed to a liquid dust catching adhesive composition that includes a component that imparts smoke and flame resistance, that is preferably a mixture of phosphoric and boric acids containing at least 50 wt. % phosphoric acid, and that may additionally include a neutralizing base that may be ammonia. Aarons et al describe a formulation containing a water-soluble alkali metal borate or boric acid, a weakly basic, water-soluble nitrogenous compound, and at least one ammonium salt that may be diammonium phosphate or monoammonium phosphate.
Also known is a flame retardant ammonium pentaborate that is said to be non-corrosive to copper, steel and aluminum. This compound is disclosed in Chemical and Engineering News, pp. 36-37 (Feb. 20, 1984).
Although certain presently available fire retardant compositions show improvement with respect to corrosiveness to metals, there is a need for a water soluble fire retardant composition that will afford a fire retarded material, in particular fire retarded wood, of low corrosiveness by using pH control, not a corrosion inhibitor, to lower corrosion. For purposes of this description of my invention, by the term "low corrosiveness" is meant that corrosiveness of the fire retarded material to a metal such as steel, brass or aluminum is less than the corrosiveness of the same material treated with the flame retardant composition of Example 1 of the Aarons et al patent without the corrosion-inhibiting dicyandiamide component thereof. Thus, the discovery of such a fire retardant composition would constitute a significant contribution to the art. Such a composition would contribute even further to the art if it were less corrosive to steel equipment than to more expensive brass equipment, as steel equipment could be used in preparing a fire retarded material.